package com.atguigu.distributed.lock.leecode;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * 力扣中等17：电话号码的字母组合
 */
public class LetterCombinations {
    public List<String> letterCombinations(String digits){
        List<String> combinations = new ArrayList<>();
        if(digits.length()==0){
            return combinations;
        }
        Map<Character,String> phoneMap = new HashMap<Character,String>(){{
            put('2',"abc");
            put('3', "def");
            put('4', "ghi");
            put('5', "jkl");
            put('6', "mno");
            put('7', "pqrs");
            put('8', "tuv");
            put('9', "wxyz");
        }};
        backtrack(combinations,phoneMap,digits,0,new StringBuffer());
        return combinations;
    }
    public void backtrack(List<String> combinations, Map<Character,String> phoneMap,String digits,int index,StringBuffer combination){
        if(index==digits.length()){
            combinations.add(combination.toString());
        }else {
            char digit = digits.charAt(index);
            String letters = phoneMap.get(digit);
            int lettersCount = letters.length();
            for (int i = 0; i < lettersCount; i++) {
                combination.append(letters.charAt(i));
                backtrack(combinations,phoneMap,digits,index+1,combination);
                combination.deleteCharAt(index);
            }
        }
    }
}
